Amber Coston-Senior Honors Thesis - The Ohio State University

23 Pages·2006·0.57 MB·English

by  Amber Dawn

Cancer Vaccine and Therapy

A Senior Honors Thesis

Presented in Partial Fulfillment of the Requirements for graduation with distinction in
Molecular Genetics in the undergraduate colleges of The Ohio State University

by

Amber Dawn Coston

The Ohio State University
June 2006

Project Advisor: Dr. Michael A. Caligiuri, Department of Internal Medicine, Division of
Hematology & Oncology, Comprehensive Cancer Center, College of Medicine and
Public Health

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Background

Research has demonstrated a relationship between cancer and the human
immune system. Certain cancers have a higher incidence in patients with compromised
immune systems. An example occurs in organ transplant patients who are taking
immunosuppressive drugs and go on to develop post-transplant lymphoproliferative
disease (PTLD). PTLD complicates between 2% and 20% of solid organ transplants
performed annually in the United States and is associated with the Epstein-Barr Virus
(EBV) infection in 95% of the cases.

Epstein-Barr Virus
EBV is the best known and most widely studied herpes virus and was also the
first virus implicated in a human cancer. EBV is associated with other cancers, such as
Burkitt’s lymphoma, Hodgkin’s disease, and Kaposi’s sarcoma. A unique feature of the
virus is that it is present, although dormant, for the lifetime of 90% of immunocompetent
adults. EBV infection can arise during childhood and adolescence and occurs as
infectious mononucleosis (“mono”) in 50% of these humans. Healthy immune systems
create T cells (immune cells in the blood) that are capable of controlling the EBV
infection. T cells become specific for EBV by recognizing the peptide from EBV proteins
on the surface of an antigen presenting cell (APC) (reference figure 1). Healthy humans
are able to activate CD8+ cytotoxic T lymphocytes (CTLs) to recognize and eliminate
virus-infected cells. However, humans with compromised immune systems are unable
to produce sufficient T cells to control the infection [1].

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T cell
receptor

EBV
Peptide
Antigen Presenting Cell T cell

Post-Transplant Lymphoproliferative Disease

Post-Transplant Lymphoproliferative Disease (PTLD) is typically linked to EBV
infection and has many features of immune system malignancy. Recently, the incidence
of PTLD has been on the rise and it has emerged as a significant complication of solid
organ and cell transplantation [2]. It is characterized by uncontrolled proliferation of B
cells when post-transplant patients are undergoing immunosuppresion. PTLD presents
significant challenges for physicians because it is difficult to predict and has high
morbidity and mortality rates.
Patients undergoing organ transplants have compromised immune systems due
to the immunosuppressive medications they are prescribed in order to avoid organ-
rejection. Because of this, these patients have impaired immune function and lack the
capabilities to fight off EBV and other typically dormant viruses. Therefore, these
patients become more likely than immunocompetent humans to develop PTLD.
There are currently a variety of methods that physicians have been using to
attempt to treat PTLD. Researchers and clinicians are in need of a treatment method
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that is able to both treat the tumor and maintain an immunosuppressed state to
preserve the organ donation [3, 4, 5]. This has been attempted through the reduction of
immunosuppressive medications, radiotherapy, chemotherapy, cell therapy, antiviral
therapy, and cytokine therapy.
In a recent study, a reduced amount of immunosuppressive drugs was
administered in order to reactivate the immune system to attack the EBV-associated
tumor [6]. This did, in fact, reduce the tumor in 9 of 11 patients, but led to organ
rejection in 5 cases. This study, for the first time, showed an increase in the
CD3+CD8+ T cells in patients that went into remission. Another recent study used HLA
tetramers complexed with EBV immunodominant peptides and found that a subset of
CD3+CD8+ T cells were EBV specific [1]. They also found in a severe combined
immune deficient (SCID) mouse model system, as well as in patients, that the
expansion of an EBV protein, BZLF1 (RAK) specific CD8+ T cells, correlated with the
prevention of PTLD after a combined cytokine treatment. These findings opened a door
in the research of human cellular subsets in mediating this protective effect.
A vaccine approach to increase the quantity of T cells is a possible treatment
method that could be beneficial to many patients. Since PTLD results in mortality in 50-
70% of patients, a vaccine to reduce the frequency of infection could be especially
advantageous to organ transplant patients.

We hypothesized that a vaccine of BZLF1 protein transduced monocyte-derived
antigen presenting cells (dendritic cells) will stimulate the expansion of Epstein-
Barr Virus (EBV) BZLF1-specific cytotoxic CD8+ T lymphocytes (CTLs).
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In order to complete this, we developed two specific aims:

Aim 1 – Goal A: Synthesize a BZLF1/GST fusion protein using the Glutathione S-
transferase (GST) gene fusion system from prokaryotic cells.
Goal B: Synthesize a BZLF1/ V5-His fusion protein from mammalian cells.
Aim 2: Determine if monocyte-derived DCs pulsed with BZLF1 fusion proteins stimulate
expansion of EBV BZLF1-specific CTLs.

Methods

Preparation of the Target Protein

The preparation and purification of BZLF1, an EBV viral protein, was
accomplished using standard protocols provided by Novagen and Invitrogen
Corporation for Goals A and B respectively (reference flow sheet 1). For Goal A, EBV
BZLF1 cDNA was cloned into a prokaryotic expression vector, pET, obtained from
Abgent Inc.
For Goal B, a mammalian expression vector, pUB6/V5-His, was prepared by
digestion with restriction enzymes (EcoR1 and BamH1) and dephosphorylation with calf
intestinal alkaline phosphatase. The vector was then gel purified. Next, the insert DNA
containing a BZLF1 coding sequence was prepared. This was accomplished by plasmid
prep and PCR (in order to amplify the BZLF1 coding sequence). This was followed by a
restriction digest with (EcoR1 and BamH1) and gel purification. The DNA insert was
then ligated into the pUB6/V5-His vector.
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For both Goals A and B, each insert/vector pair was transformed into the DH5α
strain of E. coli cells. These cells served as an expression host. Finally, the expression
of BZLF1 was analyzed. A positive clone was sequenced and the expression of BZLF1
protein was detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis
(SDS-PAGE) and a Western blot. The positive clones of generated stable Chinese
Hamster Ovarian (CHO) cell lines were expanded in order to generate a large quantity
and cell pellets were frozen at -80˚C until purification took place.

Purification of the Target Protein

For Goal A, the BZLF1 was purified following a standard protocol (GST
purification kit from Amersham Bioscience).
For goal B, the BZLF1 was purified following standard protocol provided by
Invitrogen’s ProBond Purification System. The cell lysate was prepared under native
conditions and added to a prepared His affinity column. The lysate was allowed to bind
to the resin, then the column was washed, and the protein was eluted. The protein
concentration was measured at UV280 and the eluted fractions were stored at 4˚C.
Samples of the lysate and wash supernatants were also saved for SDS-PAGE analysis.

Functional test of the Purified Target Protein
Next, functional testing of the purified BZLF1 protein was conducted (reference
flow sheet 2). First, monocyte-derived dendritic cells transduced with BZLF1 protein
were generated by culturing hPBMC for 3 days, with cytokine GM-CSF and IFN-α in the
presence of EBV BZLF1 protein. BSA (Bovine Serum Proteins) served as a negative
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control. The presence of the BZLF1 protein in the dendritic cells was determined by
immunohistochemistry staining. Next, dendritic cells transduced with BZLF1 were co-
cultured with hPBMC from the same donor (autologous). Following the culture, BZLF1-
specific T cells were expanded. The activation and cytotoxicity of the generated BZLF1-
specific T cells was also determined. The activation of CD8+ T cells was determined by
IFN-γ secretion assayed by an IFN-γ-Elispot or by intracellular IFN-γ staining. The
cytotoxicity of CD8+ BZLF1-specific T cells was determined by co-cultured CD8+ T cells
with a 51Cr-labeled B cell line derived from the same donor. The cytotoxicity of T cells
was then calculated based on the percentage of 51Cr released.

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Preparation and Purification of the Target Protein

Flow Sheet 1 (Goal B specifically)

Process Detail

Prepare pUB6/V5-His Vector 1. Digest with restriction enzyme
↓ and dephosphorylate
2. Gel purify

Prepare Insert DNA 1. Plasmid prep and PCR
(BZLF-1 coding sequence) 2. Restriction digest
3. Gel purify
↓

1. Ligate or anneal insert with
Clone Insert into pUB6/V5-His Vector
pUB6/V5-His vector

2. Transform into non-expression
host
3. Identify positive clones; colony
↓
PCR, prepare plasmid DNA,
verify reading frame by
sequencing, or in vitro

transcription/translation

Transform into Expression Host

(E. coli)
1. Transform DH5α E. coli cells
↓

Analysis of BZLF1 Expression
And 1. Detect target protein by SDS-
Generate CHO stable cell lines PAGE, Western blot
↓

Scale-up

↓
1. Scale up culture
2. Prepare extract
Purify Target Protein
3. His Affinity column purification

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Test of the Purified Target Protein

Flow Sheet 2

Process Detail

Generation of monocyte-derived DCs 1. Culture hPBMC short term (5
transduced with BZLF1 protein days) with GM-CSF in the
presence of EBV BZLF1 protein.
2. The presence of BZLF1 protein in
DCs will be determined by an
↓
immunohistochemistry staining.
3. Co-culture BZLF1+ DCs with

hPBMC from same donor
Expansion of BZLF1 specific T cells

↓
4. The activation of CD8+ T cells
can be determined by IFN

gamma secretion assayed by a
Determination of activation and
gamma IFN-Elispot.
cytotoxicity of generated BZLF1 specific

T cells
5. The cytotoxicity of CD8+ BZLF1

specific T cells will be determined

by co-cultured CD8+ T cells with

a 51Cr labeled same donor

derived B cell line. The

cytotoxicity of the T cells will be

calculated based on the

percentage of 51Cr released.

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Results

The intention of Aim 1-Goal B was to synthesize EBV BZLF1-GST fusion protein
in vitro. In order to generate a BZLF1 protein fused with the GST tag, EBV BZLF1 full
length cDNA was amplified by Polymerase Chain Reaction (PCR) and cloned into a
vector (pET vector, figure 1). The pET vector was prepared by digestion with restriction
enzymes (BamHI and HindIII) and dephosphorylation with calf intestinal alkaline
phosphatase. The vector was then gel purified. The cloning was successful as
evidenced by many more colonies produced from ligation in the presence of the insert
compared with the negative control. The positive clones were identified by colony PCR
and restriction enzyme digestion.

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